OnlyOffice hides the fact that it’s Russian.

And is it fully compatible? Most Excel-alikes have at least some hiccups.

Firefox has effectively become spyware, and so, yes, it ***should *** be replaced. There are several forks that work well. I’m using Floorp (stupid name, but really nice with some improvements over vanilla Firefox). Zen is another one gaining in popularity. Try them out! Don’t let Mozilla walk away with your data.